This invention relates to the preparation of storage-stable lacquer resins which can be baked without yellowing.
When the reaction products of amino-s-triazines, such as, for example, melamine or alkylguanamines and arylguanamines with relatively long-chain aldehydes, such as n-butanal or i-butanal, such as disclosed, for example, in U.S. Pat. No. 3,806,508, are used as a component of baking lacquers based on alkyd resins, they impart to these resin systems valuable properties, such as, for example, good storage stability, a high reactivity and a low baking temperature. However, such prior art lacquer resins composed of melamine components and alkyd components suffer from the disadvantage that they tend to discolor or to yellow at the required baking temperature or just above these, so that it has not been possible in the past to obtain pure white or light color shades which remain true to color using these surface lacquers. Hitherto, successful measures to avoid this quality defect have not been disclosed.
Surprisingly, it has now been found that the undesirable yellowing effect may be avoided without impairing the above-mentioned good properties, when the tris- or bis-alkoxyalkylamino-s-triazine is subjected to a thermal treatment before it is reacted with the alkyd resin component, acrylic resin component or epoxy resin component to give the lacquer resin. In this thermal treatment of the triazine derivative, either the solid powdered product or a suspension in a suitable solvent, if necessary under pressure, is heated. Under certain circumstances, heating of the solid may be carried out in an inert gas stream or in vacuo.